ML19322B719

Forwards from Gf Sowers,Law Engineering Testing Co,Supplementing Re Jocassee Dam Stability During Earthquakes.Dam Will Remain Intact W/Horizontal Acceleration of 0.12 G

ML19322B719
Person / Time
Site:	Oconee
Issue date:	01/14/1977
From:	Parker W DUKE POWER CO.
To:	Rusche B Office of Nuclear Reactor Regulation
References
NUDOCS 7912050721
Download: ML19322B719 (4)

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NRC FOxu 195 U1 NUCLEAR REGULATORY

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oATE OF ooCUMENT Duke Power Company 1/14/77 Mr. Benard C. Rusche Charlotte, North Carolina oATE RECsivEo Mr. William O. Parker, Jr.

1/17/77 MLETTER CNOToR.tEo PROP INPUT FORM NUMBER OF COPIES RECE6VEo 20"'G'N A' 531J NC L ASSi> : E o One signed OCoPv oESCHIPTION ENCLOSURE Ltr. w/ attached....re their 10/1/76 ltr.

and 9/21/76 meeting.... furnishing ltr. from Law Engineering Testing Co. to Duke Power Co. concerning stability of Jocassee Dam during earthquakes....

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. ACKNOWLEDGED PLANT NAME:

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Dear Sir:

My letter of October 1, 1976 provided certain information regarding the Jocassee Dam.

This information was requested by members of your staff in a September 21, 1976 meeting. Subsequently, it has been determined that the maximum seismic acceleration for which the Jocassee dam should be designed for is 0.12 g due to a 5.6 ML seismic event in the Jocassee area. Stability analyses have been completed using the pseudo dynamic approach with parameters deduced from tests made during construction.

These analyses demonstrate that the dam will remain intact with a hori-zontal acceleration of 0.12 g.

The Jocassee Dam Consulting Board is in agreement with these conclusions.

The attached December 27, 1976 letter from Mr. G. F. Sowers, Law Engineering Testing Company (Consultant to Duke Power Company) is provided to supplement that information previously submitted.

Very truly yours,

' e = he William O. Parker, Jr.

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LAW ENGINEERING TESTING COMPANY Ge. technical and Materials Engineers 2600 f;ENTIIRY PARrWu. N L.I SUIT E 425i P. O. BOX 98008 t ATLANTA, GEORGIA 30329I(404) 325 3933 GEORGE F. S0WERS. P.E.

consuitant December 27, 1976 Mr. R. S. Bhatnagar Senior Engineer Duke Power Company 422 South Church Street Charlotte, North Carolina 28242

SUBJECT:

Stability of Jocassee Dam During Earthquake.s

Dear Mr. Bhatnagar:

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As discussed at the recent Consultants Meeting and as indicated in the Law Engineering Test Report regarding the reservoir-induced seismicity at Jocassee, it appears that the maximum effective earthquake for design,

purposes at Jocassee Dam should be 0.12g.

Although not specifically stated in the Law Engineering Test Report, the 0.12g does not represent the maximum possible acceleration. There may be infrequent " spikes" of short duration, high acceleration. However, con-sidering the inertia of the embankment mass, such high acceleration, ;hort duration bursts of energy would have little effect except J:o dislodge occasional pieces of riprap.

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We have been informed by telephone that stability aaalyses have been completed by Duke Power Company using the psuedo-dynamic approach in which

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a steady state acceleration is introduced instead of the cycles of random motion ordinarily associated with earthquakes.

It has been our experience that such analyses are of reasonable validity when the earthquake accelera-tions do not exceed 0.2g.

You informed us that your stability analyses, utilizing the strength parameters deduced from tests made during construction and the earthquake analysis, indicate the dam will not fall with a horizontal acccleration of 0.12g.

Based on the present state of the art, this should be adequate.

However, I should like to examine the critical circles derived from this analysis. Very shallow circles are merely simulations of " sheet" failure.

Obviously, a rock slope which has been placed at an angle equal to the angle of internal friction can only have a safety factor of 1.0.

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LAW ENGINEERING TESTING COMPANY December 27, 1976 Page Two 4

as the behavi' oral history of many a rockfill dam is illustrated, this safety factor of 1.0 against sheet failure is entirely adequate provided subsequent movement does not induce shear of the core, followed by over-topping.

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